Electromagnetically actuated valve

ABSTRACT

A fuel injection valve for use in fuel injection systems of compressed-mixture, externally ignited internal combustion engines has a core provided with a wear-resistant layer that has a greater layer thickness than a layer thickness of a wear-resistant layer of an armature facing the core. This greater layer thickness is present at least in an immediate contact area between the core and the armature.

BACKGROUND INFORMATION

The present invention relates to an electromagnetically actuated valve.Several electromagnetically actuated valves, in particular fuelinjection valves, are known where components subject to wear areprovided with wear-resistant coatings.

German Published Patent Application No. 29 42 928 describes theapplication of wear-resistant diamagnetic material coatings on partssubject to wear, such as armatures and nozzle bodies. These coatings,applied in accurately dimensioned layer thicknesses, are used to limitthe stroke of the valve, thereby minimizing the effect of residualmagnetism on the movable parts of the fuel injection valve.

European Published Patent Application No. 0 536 773 also describes afuel injection valve where a hard metal coating is applied byelectroplating to the armature of its cylindrical peripheral surface andannular stop surface. This coating, made of chromium or nickel, has athickness of 15 to 25 μm, for example. As a result of electroplating, aslightly tapered layer thickness distribution is formed with a minimallythicker layer achieved at the outer edges. The layer thicknessdistribution of coatings formed by electroplating is physicallypredefined and can barely be influenced.

SUMMARY OF THE INVENTION

The valve according to the present invention has the advantage that acost-effective stop region is created in a simple manner. According tothe present invention, in which the wear-protection layer applied on thestationary core is thicker than the wear-protection layer applied on theaxially moving armature, it is also possible to increase the magneticforce of the electromagnetic circuit of the valve. Since in the case ofelectroplated layers leakage is reduced at smaller set values of thelayer thickness, smaller effective residual air gap fluctuations occurin the core/armature area. Thus, the fluctuations of the injected fuelamount q_(dyn) are advantageously reduced, while the minimum operatevoltage values are increased.

Wear on the movable armature is considerably less than on the stationarycore, and thus a much thinner wear protection layer can be applied tothe armature without affecting the quality, which results in anon-negligible coating material savings. Furthermore, coating times areadvantageously reduced, in particular when coating the armature.Material savings result in cost reduction, which is further enhanced bythe reduced disposal costs for the electroplating baths.

Another advantage results from the reduced scatter of the armaturediameter, which favorably affects the wear characteristics due to theresulting reduced guidance play.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a fuel injection valve according to the present invention.

FIG. 2 shows a detail of the injection valve stop in the region of thecore and armature provided with wear protection layers.

DETAILED DESCRIPTION

The electromagnetically actuated valve shown as an example in FIG. 1, inthe form of an injection valve for fuel injection systems ofcompressed-mixture, externally ignited internal combustion engines, hasa core 2, serving as a fuel inlet nozzle, surrounded by a magneticcoil 1. Core 2 is tubular in shape, for example, and has a constantexternal diameter over its entire length. A bobbin 3 that is stepped inits radial direction carries the winding of magnetic coil 1 and, inconjunction with core 2, allows the injection valve to have aparticularly compact design in the area of magnetic coil 1.

Concentrically with longitudinal valve axis 10, tubular metallicintermediary piece 12 is tightly connected to the lower end 9 of core 2,for example, by welding, and partially surrounds lower core end 9axially. Stepped bobbin 3 partially surrounds core 2 and, with one step15 having a larger diameter, intermediary piece 12, at least in part,axially. Downstream from bobbin 3 and intermediary piece 12, there is atubular valve seat carrier 16, which is firmly connected to intermediarypart 12, for example. A longitudinal bore hole 17 runs concentricallywith longitudinal valve axis 10 in valve seat carrier 16. A valve needle19, which is tubular, for example, and is connected, for example, bywelding, at its downstream end 20 with a spherical valve closing body21, on whose periphery five flats 22 are provided for the fuel to flowby, is arranged in longitudinal bore hole 17.

The injection valve is actuated electromagnetically in a known manner.The electromagnetic circuit with magnetic coil 1, core 2, and asocket-shaped armature 27 is used for axially moving valve needle 19 andthus for opening the injection valve against the elastic force of arestoring spring 25 and closing. Armature 27 is connected to valveneedle 19 with its end facing away from valve closing body 21 throughfirst welding seam 28 and aligned with core 2. At the downstream endfacing away from core 2 of valve seat carrier 16, a cylindrical valveseat body 29, having a fixed valve seat, is tightly mounted inlongitudinal bore hole 17 by welding.

A guide orifice 32 of valve seat body 29 is used to guide valve closingbody 21 during the axial movement of valve needle 19 with armature 27along longitudinal valve axis 10. Spherical valve closing body 21 workswith the valve seat, which is conically tapered in the direction of thefuel flow, of valve seat body 29. At its end facing away from valveclosing body 21, valve seat body 29 is concentrically and permanentlyattached to a perforated spray disk 34, which is pot-shaped, forexample. At least one, but preferably four spray orifices 39, formed byeroding or punching, are located in the bottom part of perforated spraydisk 34.

The insertion depth of valve seat body 29 with pot-shaped perforatedspray disk 34 determines the setting of the stroke of valve needle 19.One end position of valve needle 19, when magnetic coil 1 is notenergized, is determined by the contact of valve closing body 21 withthe valve seat of valve seat body 29, while the other end position ofvalve needle 19, when magnetic coil 1 is energized, is determined by thecontact of armature 27 with core end 9, i.e., exactly in the areadesigned according to the present invention, marked with a circle, andillustrated in FIG. 2 on a modified scale.

An adjusting socket 48, inserted in flow bore 46 of core 2 runningconcentrically with longitudinal valve axis 10, which is made of coiledspring steel sheets, for example, is used for prestressing restoringspring 25, which is in contact with adjusting socket 48 and whoseopposite end is in contact with valve needle 19.

The injection valve is largely surrounded by extruded plastic coating50, extending in the axial direction from core 2 through magnetic coil 1to valve seat carrier 16. An electric connector 52, extruded togetherwith plastic coating 50, is associated with this plastic coating 50.

A fuel filter 61 projects into flow bore 46 of core 2 at its intake end55 and is responsible for filtering out fuel components that by theirsize could cause clogging or damage to the injection valve.

In FIG. 2, the area marked with a circle in FIG. 1 of one end positionof valve needle 19, in which armature 27 is in contact with end 9 ofcore 2, is illustrated on a different scale. It is known that themetallic layers 65, for example of chromium or nickel, can be applied toend 9 of core 2 and to armature 27 by electroplating, for example.Layers 65 and 65' are applied both to end faces 67 and 67' runningperpendicularly to longitudinal valve axis 10 and, at least partially,to peripheral surfaces 66 and 66' of armature 27 and core 2,respectively. Layers 65, which normally have a thickness between 10 and25 μm, are shown in FIG. 2 with their layer thicknesses not to scalewith respect to the size of components 2 and 27.

For the operation of the injection valve, core 2 and armature 27 mustcome into contact in a relatively small area, for example, only in theouter area of the upper face of armature 27, which faces away fromlongitudinal valve axis 10. This requirement is achieved throughelectroplating. In electroplating, a field line concentration resultingin a minimally tapered layer distribution, for example, occurs at theedges of the parts to be electroplated, here core 2 and armature 27. Thelayers applied, 65 and 65', are therefore stressed in small areas onlyduring the operation of the injection valve.

The contact faces of the contact parts should maintain their dimensionalaccuracy to the maximum possible degree even after extended operation,so that the contact pickup and release time of armature 27 remainsapproximately constant despite some slight wear. The tolerances of thefuel amount to be injected q_(dyn) can also be kept very narrow with avery high long-term stability of the area of this contact surface.Continuous operation tests show that the movable part, armature 27, isless subject to wear than the stationary part, core 2. The depth of wearof layers 65 and 65' resulting after many years of operation can betwice to three times as great on core 2 than on armature 27, forexample. Therefore it makes sense that layer 65 on armature 27 bedesigned to be thinner in relation to layer 65' on core 2 withoutimpairing long-term stability. Especially in the case of narrowertolerances, it is recommended that core 2 be provided with a layer 65'with a greater thickness x than that of armature 27.

As one example of possible layer thicknesses x and y for layers 65 and65', we shall mention here 7 μm for core 2 and 4 μm for armature 27.These dimensions are, of course, always subject to narrow tolerances.These figures are being given for the sake of clarity only, withoutlimiting the scope of the invention. In any case, layer thickness x oflayer 65' of stationary core 2 is considerably greater than layerthickness y of layer 65 of axially movable armature 27, which means thatlayer thickness x of layer 65' of core 2 exceeds layer thickness y oflayer 65 of armature 27 by at least 25%. These figures refer only to theimmediate contact area a and a' on core 2 and armature 27, respectively,whose axial approximation area is marked with a double arrow.

Contact area a, a' is the actually wearing contact part, which has anannular shape in the ideal case and is usually sickle-shaped, i.e., hasthe shape of an annular section. Contact area a, a' usually has acontact width of 50 to 200 μm, with possible maximum widths of 300 μm.Outside contact area a, a', layers 65 and 65' can also be tapered, sothat the opposite layer thicknesses are approximately the same. Usuallylayer 65 of armature 27 has, however, a smaller thickness y thanthickness x of layer 65' on core 2; i.e., x>y, especially in the contactarea a, a'. Chromium, molybdenum, nickel or carbon carbides are normallyused as coating materials. Other coating materials normally used forcoating can, however, also be used to manufacture wear-resistant layers65, 65' on core 2 and armature 27.

What is claimed is:
 1. An electromagnetically actuated fuel injectionvalve for a fuel injection system of an internal combustion engine,comprising:a magnetic coil; a core made of ferromagnetic material andsurrounded by the magnetic coil with respect to a longitudinal axis ofthe core; and an armature aligned with respect to the core, the armaturebeing axially movable along the longitudinal axis to cause a valveclosing body to move out of a contacting relationship with respect to afixed valve seat when a contact surface of the armature is attracted toan immediate contact area of a contact surface of the core in responseto an energization of the magnetic coil, wherein:the contact surface ofthe armature is provided with a first wear-resistant layer, and thecontact surface of the core is provided with a second wear-resistantlayer facing the first wear-resistant layer, the second wear-resistantlayer having a layer thickness that is greater, at least in theimmediate contact area, than a layer thickness of the firstwear-resistant layer.
 2. The valve according to claim 1, wherein thelayer thickness of the second wear-resistant layer exceeds the layerthickness of the first wear-resistant layer in the immediate contactarea by at least 25%.
 3. The valve according to claim 1, wherein thelayer thickness of the second wear-resistant layer is greater than thelayer thickness of the first wear-resistant layer throughout a length ofeach one of the contact surface of the core and the contact surface ofthe armature.
 4. The valve according to claim 1, wherein each one of thefirst wear-resistant layer and the second wear-resistant layer istapered.
 5. The valve according to claim 1, wherein a maximum width ofthe immediate contact area is 300 μm.
 6. The valve according to claim 1,wherein each one of the first wear-resistant layer and the secondwear-resistant layer is magnetic.